Combines and other vehicles often operate in environments where the air is heavy laden with dust from the earth and plant residues which tend to cause rapid contaminant accumulation in the air filter media unless an air pre-cleaner is used to remove the bulk of the airborne particulate matter. Traditional engine combustion air pre-cleaners use a variety of methods to generate a cyclonic action which tends to separate the particulate matter from the air by way of differences in inertial loadings along curved trajectories. Since the particulate matter has a higher density than does the air, the particulate matter accumulates further outboard of the centrifugal axis of the body of the pre-cleaner device through which air is being circulated along a curved path going about the axis. While these devices effectively remove the particulates from the combustion air, they suffer from the drawback that a large pressure drop occurs between the air inlet and outlet which inhibits air flow into the engine, robbing it of power.
One known combustion air pre-cleaner developed for addressing the problem of engine power loss due to the engine having to overcome a large pressure drop in the combustion air as it passes through the body of the pre-cleaner device is disclosed in U.S. Pat. No. 6,921,424, wherein a cylindrical tubular body of a pre-cleaner device is constructed with an air inlet and an air outlet disposed along the longitudinal axis of the body, with a substantially egg-shaped body being disposed axially within the body just upstream of a conical end of an outlet tube mounted for being adjusted axially within the body so as to vary the restriction defined between the downstream end of the egg-shaped body and the end of the outlet tube, the amount of restriction being determined in accordance with the combustion air requirement of the particular engine being used so as to minimize the pressure drop across the pre-cleaner. The problem with this patented pre-cleaner is that it is designed for an automobile engine and does not take into account the large range of load conditions imposed on an engine used in an off-road applications, such as that imposed on a combine harvester engine during a typical harvesting operation, for example.
The problem that presents itself then is that of providing a cyclonic type pre-cleaner which is operable for supplying pre-cleaned combustion air to an engine while not robbing power from the engine throughout normal operating conditions where the load imposed on the engine varies considerably.